Ultrasonic motor having high drive efficiency

ABSTRACT

An ultrasonic motor has a stator having a piezoelectric member vibrated by a drive signal, and an elastic member for generating traveling vibration wave in a drive surface thereof upon vibration of the piezoelectric member, a rotor which is urged against the drive surface of the elastic member and is driven by the generated traveling vibration wave, a support member integrally molded on the elastic member, and a fixing member for holding the support member. In the ultrsonic motor, one end face of the support member is formed at the same level as the drive surface or the junction surface of the elastic member, an electrode of the piezoelectric member is grounded through the support member, a plurality of holes are regularly formed in the circumferential direction of the support member, or the support member is fixed to the fixing member by an adhesive, thereby improving drive efficiency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ultrasonic motor having high driveefficiency, which causes a stator to generate a traveling vibrationwave, thereby driving a rotor. More particularly, the present inventionrelates to an ultrasonic motor having high drive efficiency, whichcauses an elastic member to generate a traveling vibration wave uponvibration having a vibration frequency in an ultrasonic range of apiezoelectric member, thereby driving a rotor.

2. Related Background Art

The structure of a conventional ultrasonic motor is disclosed in, e.g.,JP-A-62-77068. FIG. 6 is a sectional view of the ultrasonic motor. Astator 1 is constituted by integrally fixing a piezoelectric member 1bto an elastic member 1a. A radial support member 3 is integrally moldedon an inner peripheral surface of the elastic member 1a near a neutralaxis of the stator 1 as a whole. The support member 3 has a thin plateportion 3a provided to the inner peripheral surface of the elasticmember 1a, and a thick portion 3b provided on the peripheral edge of thethin plate portion 3a and having a larger thickness than that of thethin plate portion 3a. A technique for integrally molding the supportmember to the elastic member in this manner is also disclosed in, e.g.,JP-A-59-213286. The thick portion 3b is fixed in a case 5 which receivesa bearing 4.

A flange portion 6a radially projects from the inner periphery of therotor 2, and a thick portion 6b is integrally molded on the peripheraledge of the flange portion 6a. A compression force by a given means (notshown) is applied to the thick portion 6b through a bearing 7, so that alower surface 8 of the rotor 2 is urged against a drive surface 1c ofthe elastic member 1a.

When an AC voltage is applied to the piezoelectric member 1b, thepiezoelectric member 1b causes bending vibration, and a travelingvibration wave is generated in the elastic member 1a. This vibrationwave frictionally drives the rotor 2. The generation mechanism of thetraveling vibration wave is described in detail in JP-A-60-245482 and adescription thereof will be omitted.

In the above structure, when the thick portion 3b of the support member3 is fixed by a pressing 40 and a fixing cylinder 50 or theirequivalents shown in FIG. 2, the following problems are posed. If alower end face 3c of the thick portion 3b of the support member 3 is notflat, when the thick portion 3b is fixed by the pressing 40 and thefixing cylinder 50 shown in FIG. 2, an internal stress is generated inthe elastic member 1a, thus decreasing drive efficiency of theultrasonic motor. On the other hand, if a junction surface 1d of theelastic member 1a contacting the piezoelectric member 1b is not flat,when the piezoelectric member 1b is fixed to the elastic member 1a, aninternal stress is generated in the elastic member 1a, and alsodecreases drive efficiency of the ultrasonic motor. As shown in FIG. 6,when the lower end face 3c of the thick portion 3b and the junctionsurface 1d of the elastic member 1a do not exist on the same plane, itis almost impossible to simultaneously polish these surfaces.

The structure of a conventional stator is disclosed in, e.g.,JP-A-60-245482. FIGS. 10 and 11 show this structure. A stator 10 isconstituted by adhering an annular elastic member 11 and an annularpiezoelectric member 12. A plurality of electrodes 13 (FIG. 11) areformed on the upper surface of the piezoelectric member 12, andelectrodes 14a to 14d are also formed on its lower surface. The elasticmember 11 is adhered to the piezoelectric member 12 so as to beelectrically connected to all the electrodes 13. These electrodes aremagnetized to alternately have opposite polarities. One-end portions oflead wires 15 and 16 are respectively soldered to the electrodes 14a and14b. An AC voltage is applied to the electrodes 14a and 14b throughthese lead wires 15 and 16. The other end of a lead wire 17, one end ofwhich is grounded, is soldered to the electrode 14c. The electrode 14cis electrically connected to the elastic member 11 through a conductiveadhesive 18.

In the above-mentioned structure, all the electrodes 13 are groundedthrough the elastic member 11, the conductive adhesive 18, the electrode14c, and the lead wire 17. Therefore, when an AC voltage is applied tothe electrodes 14a and 14b, this is equivalent to apply a voltage to thewidthwise direction of the piezoelectric member 12. When a predeterminedAC voltage is applied to the electrode 14a through the lead wire 15, andan AC voltage having a 90° phase difference from the predeterminedvoltage is applied to the electrode 14b through the lead wire 16, thepiezoelectric member 12 is vibrated by these applied voltages. Upon thisvibration, a traveling vibration wave is generated in a drive surface11a of the electric member 11.

However, in this structure, the elastic member 11 and the electrode 14care electrically connected through the conductive adhesive 18 to groundthe electrodes 13. Therefore, the adhesive 18 is degraded by vibrationof the elastic member 11 in resulting in a grounding error of theelectrodes 13. Since ultrasonic vibration has a high frequency, it has apeeling effect as demonstrated in ultrasonic washing. Thus, the groundlead wire 17 may be directly connected to the elastic member 11 througha screw or the like so as not to disconnect the lead wire 17. However,undesirable vibration occurs in the connected portion due to the weightof the screw, and as a result, smooth driving is disturbed.

In some motors, as disclosed in Japanese Patent Laid-Open (Kokai) No.59-178988, a comb-like groove is formed in the drive surface of theelastic member to improve drive efficiency.

As a support method of the stator, the following methods are known:

(1) A method of supporting the stator by arranging a shock absorber suchas a felt on the lower surface of the piezoelectric member;

(2) A method of supporting the stator by arranging a flange-like supportmember extending from an outer or inner peripheral surface of the statornear a neutral surface and clamping the support member by fixingmembers; and

(3) A method of supporting the stator by arranging a plurality ofrod-like sub vibration members radially extending from the outer orinner peripheral surface of the stator near a neutral surface, andplacing the distal ends of the vibration members on the support member,as disclosed in Japanese Patent Laid-Open (Kokai) No. 60-96183(corresponding to U.S. Pat. No. 4,634,915).

However, in the method (1) of supporting the stator by the felt, thefelt has poor weather resistance, and a drive condition largely changesdue to aging of the felt, resulting in poor reliability. In the method(2) of supporting the stator by the flange, since a bending strength ofthe flange portion cannot be lowered, drive efficiency is decreased. Inaddition, in the method (3) of supporting the stator by the rod-like subvibration members, since a large number of rod-like sub vibrationmembers having a small width and thickness must be arranged to have highdimensional precision, and are difficult to work, resulting an expensivestructure. If each rod-like sub vibration member is thick, itsmechanical strength is increased, and the vibration of the stator isexternally transmitted through the support member, resulting ingeneration of noise.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve drive efficiency ofan ultrasonic motor by reducing an internal stress generated in anelastic member when a support member of the elastic member is clampedand fixed by fixing members.

It is another object of the present invention to improve driveefficiency of an ultrasonic motor by improving durability of a slidermember of a rotor which is frictionally driven on an elastic member andby improving weather resistance caused by a change in environmentalcondition such as a temperature, humidity, and the like.

It is still another object of the present invention to improve driveefficiency of an ultrasonic motor by preventing a grounding error ofelectrodes formed on a stator caused by unnecessary vibration generatedin an elastic member.

It is still another object of the present invention to improve driveefficiency of an ultrasonic motor and to prevent generation of noise bydecreasing a bending strength of a support member of an elastic memberto improve a vibration condition of the elastic member.

It is still another object of the present invention to improve driveefficiency of an ultrasonic motor and to prevent generation of noise byeliminating a support loss of a support member of an elastic member.

In order to achieve the above objects, according to the presentinvention, there is provided an ultrasonic motor having a statorconsisting of a piezoelectric member and an elastic member, a rotorwhich is brought into contact with the stator under pressure, a supportmember for holding the stator, and a fixing member, the support memberconsisting of a thin plate portion and a thick portion being integrallymolded on an outer or inner peripheral surface of the elastic member,wherein one end face of the thick portion is formed at the same level asa drive surface or a junction surface of the elastic member with thepiezoelectric member. Thus, the junction surface of the elastic memberwith the piezoelectric member and one end face of the thick portion ofthe support member can be simultaneously polished. The drive surface ofthe elastic member and the other end face of the thick portion of thesupport member can be simultaneously polished. Therefore, the junctionsurface of the elastic member and one end face of the thick portion, orthe drive surface of the elastic member and the other end face of thethick portion can be kept flat. Even if the thick portion is clamped andfixed by the fixing members, no internal stress is generated in theelastic member, thus improving drive efficiency of an ultrasonic motor.

In order to achieve the objects of the present invention, the elasticmember of the stator is formed of an invar material, and a slider memberof the rotor is formed of a material containing polytetrafluoroethylene(PTFE), thereby decreasing wear of the slider member of the rotor andincreasing a durability-limit rotation count. In addition, the slidermember can be prevented from being stuck to the elastic member due to anincrease in temperature or humidity. In this manner, the durability andweather resistance of the rotor are improved to improve drive efficiencyof the ultrasonic motor.

In order to achieve the objects of the present invention, there is alsoprovided an ultrasonic motor in which a first electrode is arranged on asurface of a piezoelectric member on a side contacting an elasticmember, a second electrode is arranged on an opposite surface, the firstelectrode is grounded through the elastic member, and an AC voltage isapplied to the second electrode to vibrate the piezoelectric member,comprising grounding means for grounding the first electrode through asupport member integrally formed on the outer or inner peripheralsurface of the elastic member. With this structure, when thepiezoelectric member vibrates and a traveling vibration wave isgenerated in the elastic member, a grounding error of the firstelectrode can be prevented, thus improving drive efficiency of theultrasonic motor.

In order to achieve the object of the present invention in an ultrasonicmotor of the present invention, a plurality of holes are regularlyformed in a circumferential direction in a support member which isintegrally formed on a side surface of an elastic member. In addition,in the ultrasonic motor of the present invention, a comb-like groove isformed in the elastic member, and a plurality of holes are periodicallyformed in the support member integrally formed on the side surface ofthe elastic member in association with the cycle of the comb-likegroove. Thus, the bending strength of the support member can bedecreased, and the vibration condition of the elastic member isimproved. Therefore, drive efficiency of the ultrasonic motor can beimproved, and generation of noise can be prevented.

Furthermore, in order to achieve the objects of the present invention,there is also provided an ultrasonic motor in which a support memberintegrally arranged on a side surface of an elastic member is clampedand fixed by a pressing and a fixing cylinder, wherein the supportmember is adhered to at least one of the pressing and the fixingcylinder by an adhesive. With this structure, the support loss of thesupport member can be eliminated, thus improving drive efficiency of theultrasonic motor, and preventing generation of noise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show an embodiment of an ultrasonic motor according to thepresent invention, in which FIG. 1 is an exploded sectional view of themotor, and FIG. 2 is a sectional view of the motor after assembly;

FIG. 3 shows an amplitude of a vibration wave acting on an elasticmember and a support member in the embodiment shown in FIGS. 1 and 2;

FIG. 4 is a sectional view showing another embodiment of an elasticmember and a support member constituting an ultrasonic motor accordingto the present invention;

FIG. 5 is a sectional view showing another embodiment of an ultrasonicmotor according to the present invention;

FIG. 6 is a sectional view showing a structure of a conventionalultrasonic motor;

FIG. 7 is a sectional view showing still another embodiment of anultrasonic motor according to the present invention;

FIG. 8 is a sectional view showing another embodiment of a stator, asupport member, and a fixing member constituting the ultrasonic motoraccording to the present invention;

FIG. 9 is a sectional view showing still another embodiment of anultrasonic motor according to the present invention;

FIGS. 10 and 11 show a structure of a conventional stator, in which FIG.10 is a perspective view thereof, and FIG. 11 is a sectional viewthereof;

FIGS. 12 and 13 are perspective views showing another embodiment of arotor a stator and a support member constituting the ultrasonic motoraccording to the present invention;

FIG. 14 shows an amplitude of a vibration wave acting on the stator andthe support member in the embodiment shown in FIG. 13;

FIGS. 15A to 15G show patterns of a comb-like groove and a plurality ofholes formed in the elastic member and the support member in theembodiment shown in FIG. 13; and

FIG. 16 is a sectional view showing another structure of holes formed inthe support member in the embodiment shown in FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereinafterwith reference to FIGS. 1 to 3.

FIG. 1 is an exploded sectional view of an ultrasonic motor according tothe present invention, and FIG. 2 is a sectional view thereof afterassembly. A stator 100 is constituted by a ring-like elastic member 101,and a ring-like piezoelectric member 102 adhered to a junction surfaceP2 of the elastic member 101. A drive surface P1 of the elastic member101 has a flatness tolerance of 0.5 μm or less by polishing. A radialflange-like support member 30 is integrally formed on the elastic member101 by cutting the elastic member 101 from its outer peripheral surfacenear a neutral surface of the stator 100 as a whole. The support member30 has a 0.3-mm thick thin plate portion 31 contiguous with the outerperipheral surface of the elastic member 101, and a thick portion 32contiguous with the thin plate portion 31. The thickness of the thickportion 32 is sufficiently larger than that of the thin plate portion31. In this embodiment, a lower end face P3 of the thick portion 32 isat the same level as the junction surface P2 of the elastic member 101.

The junction surface P2 of the elastic member 101 must be finished tohave the same flatness as that of the drive surface P1 by polishingsince it must be electrically connected to all the electrodes of thepiezoelectric member 102 when it is adhered to the piezoelectric member102. In this embodiment, since the junction surface P2 and the lower endface P3 of the thick portion 32 are at the same level, the end face P3can be simultaneously polished upon polishing of the junction surfaceP2. In addition, a surface P5 of the pressing 40, which is brought intocontact with the polished end face P3 is also subjected to polishing.

A rotor (movable element) 20 comprises a ring-shaped rotor base 21, anda slider member 22 adhered to the rotor base 21. A lower surface P6 ofthe slider member 22 is polished to the same flatness as that of thedrive surface P1 after the slider member 22 is adhered to the rotor base21, so that the lower surface P6 can be in uniform contact with thedrive surface P1 of the elastic member 101.

As shown in FIG. 2, after the piezoelectric member 102 is adhered to thejunction surface P2 of the elastic member 101, the pressing 40 isthreadably engaged with the fixing cylinder 50, so that the upper andlower end faces P4 and P3 of the thick portion 32 of the support member30 are clamped between a surface P7 of the fixing cylinder 50 and thesurface P5 of the pressing 40. In this case, since the lower end face P3of the thick portion 32 and the surface P5 of the pressing 40 have beenpolished, even if the surface P7 of the fixing cylinder 50, which isdifficult to be polished, is merely lathed, i.e., even if the surface P7does not have high flatness, the flatness of the drive surface P1 of theelastic member 101 will not be degraded.

In this embodiment, the pressing 40 has a larger thickness than that ofa surface P7 portion of the fixing cylinder 50, and the thick portion 32of the support member 30 is clamped by the pressing 40 and the fixingcylinder 50, so that the influence of the stress acting on the elasticmember 101 is determined by a contact state between the surface P5 ofthe pressing 40 and the surface P3 of the thick portion 32.

The slider member 22 is adhered to the rotor base 21, and the lowersurface P6 of the slider member 22 is urged against the drive surface P1of the elastic member 101 by a pressing member (not shown).

When an AC voltage (drive signal) is applied to the piezoelectric member102 in this state, the piezoelectric member 102 causes bendingvibration, and a traveling vibration wave is generated in the drivesurface of the elastic member 101. Thus, the vibration wave drives therotor 20. In this case, the amplitude of the vibration wave acting onthe support member 30 and the elastic member 101 is as shown in FIG. 3.More specifically, since the thick portion 32 is fixed at a contiguousportion between the thin plate portion 31 and the thick portion 32, theamplitude is almost zero, and the amplitude of the thin plate portion 31is increased as getting closer to the elastic member 101. The amplitudenear the central portion of the elastic member 101 is maximum.Therefore, even if the thick portion 32 having a large thickness isarranged, drive efficiency of the ultrasonic motor will not be decreasedas compared to that of a conventional motor.

Since the junction surface P2 of the elastic member 101 and the end faceP3 of the thick portion 32 are at the same level, the end face P3 can besimultaneously polished upon polishing of the junction surface P2. As aresult, efficiency of a polishing operation can be improved. Morespecifically, in polishing, a member to be worked is polished whilerotating it on a polishing plate which is finished to have highflatness. In order to polish the surfaces P2 and P3 with steps, a workof a surface at a lower step is difficult and inefficient. In thisembodiment, since the surfaces P2 and P3 can be simultaneously polishedin a single polishing operation, it is very efficient as compared to acase wherein surfaces P2 and P3 are worked with steps, and easymass-production can be expected.

FIG. 4 shows another embodiment wherein a thick portion 35 of a supportmember 33 also projects on the side of the drive surface P1 of theelastic member 101, and its upper end face P40 is worked at the samelevel as the drive surface P1. In this case, the end face P40 can besimultaneously polished when the drive surface P1 is polished. In thiscase, the positions of the pressing 40 and the fixing cylinder 50 arereversed to hold the stator 100. More specifically, the surface P5 ofthe pressing 40 is in contact with the upper end face P40 of the thickportion 35. When the thick portion 35 is clamped by the pressing 40 andthe fixing cylinder 50, no internal stress is generated in the elasticmember 101.

In the above embodiment, the support member is formed on the outerperipheral surface of the elastic member. However, as shown in FIG. 5, asupport member 36 may be formed on an inner peripheral surface of theelastic member 101. In this case, a thick portion 38 of the supportmember 36 is clamped and fixed by a pressing 41 and a fixing cylinder 51which are located on the inner periphery of the stator 100.

The material of the slider member 22 will be described in detail below.

The present applicant conducted performance tests about six slidermembers No. 1 to No. 6 shown in Table 1 upon selection of an optimalslider member therefrom. In this case, as the elastic member 101constituting the stator 100, Fe-36Ni invar was used. In the performancetests, maximum efficiency values (%) of motors were obtained, as shownin Table 2, and it was found from the test results that the slidermembers No. 1 and No. 4 to No. 6 were good in efficiency at almost thesame level. The present applicant conducted wear-resistance tests ofthese slider members No. 1 and No. 4 to No. 6, and obtained the resultsshown in Table 2. Then, it was found that the slider members No. 5 andNo. 6 were superior in terms of a wear level and a durability-limitrotation count.

The present applicant then conducted acceleration reaction tests of theslider members No. 5 and No. 6. More specifically, in an ultrasonicmotor, a slider member is always brought into contact with an elasticmember at a constant compression force. Thus, if a motor has not beenoperated for a long period of time, the slider member is stuck to theelastic member, and the motor can never be driven. In this test, inorder to check the presence/absence of sticking, the slider members No.5 and No. 6 were left in an atmosphere at a humidity of 90% and atemperature of 80° C. while being in contact with the elastic members ata constant compression force. As a result, the slider member No. 5exhibited a sticking reaction, while the slider member No. 6 did notexhibit any sticking reaction and were normally driven after the test.Performance (efficiency) using the slider member No. 6 after all thetests was almost the same as the results shown in Table 2.

Finally, the present applicant conducted a test of combining the slidermember No. 6, and a phosphor-bronze stator and a stainless-steel(SUS301) stator. As a result, it was found that the slider No. 6 wasfirmly stuck to the phosphor-bronze stator, and that it might or mightnot be stuck to the stainless-steel slider.

Thus, it was found that the slider member No. 6, i.e., a materialcontaining PTFE (80 wt. %)+glass fiber (15 wt. %)+molybdenum disulfide(5 wt. %) was most suitable for the slider member. In addition, it wasalso found that if an invar material was used as a material of a statorcombined with the slider member No. 6, the motor could be usedregardless of an atmosphere (condition); if stainless steel was used,application conditions must be limited.

                  TABLE 1                                                         ______________________________________                                        No.      Slider Member Composition                                            ______________________________________                                        1        Bismaleimide Triamine Resin + Kevlar Fiber                           2        Polyester Resin + Kevlar Fiber                                       3        Epoxy Resin + Kevlar Fiber                                           4        Polyamideimide Resin + PTFE (3 wt. %) +                                       Graphite (12 wt. %)                                                  5        Ekonol E101 (70 wt. %) + PTFE (30 wt. %)                             6        PTFE (80 wt. %) + Glass Fiber (15 wt. %) +                                    Molybdenum Disulfide (5 wt. %)                                       ______________________________________                                         PTFE: Polytetrafluoroethylene                                            

                  TABLE 2                                                         ______________________________________                                             Maximum                                                                       Efficiency          Djurability-Limit                                    No.  (%)        Wear     Rotation Count                                                                             Sticking                                ______________________________________                                        1    27.5       Large    About 180,0000                                                                             --                                                               Reversible                                                                    Rotations                                            2    17.5       --       --           --                                      3    23.0       --       --           --                                      4    28.1       Medium   About 40,000 --                                                               Reversible                                                                    Rotations                                            5    28.0       Very     About 100,0000                                                                             Yes                                                     Small    Reversible                                                                    Rotations                                            6    27.0       Very     About 800,0000                                                                             No                                                      Small    Reversible                                                                    Rotations or More                                    ______________________________________                                    

The above test results reveal the followings.

The influence of the material of the slider member to the driveefficiency of a motor has not been clear at present. The slider membersNo. 1, No. 2, and No. 3 contain the Kevlar fibers, and of these members,only the slider member No. 3 has poor efficiency. Therefore, it can beestimated that the poor efficiency is not caused by the Kevlar fiber butby a content of a polyester resin or an epoxy resin.

As can be seen from TABLE 2, in the wear resistance test, better testresults are obtained when a material having a low coefficient offriction is used. More specifically, since the slider member No. 1 doesnot contain a material having a low coefficient of friction at all, itsuffers from largest wear. Although the slider member No. 4 contains amaterial of a low frictional coefficient, i.e., PTFE, since its contentis as low as 3 wt. %, the wear is medium. However, under a normal usecondition, the member No. 4 can assure a sufficient wear resistance. Theslider members No. 5 and No. 6 contain PTFE as high as 30 wt. % and 80wt. %, respectively, and hence, they assure very small wear.

In this manner, as shown in TABLE 2, the slider member can contain 3 to100 wt. % of a material of a low coefficient of friction such as PTFE toreduce wear. In addition, it can also be estimated that if a slidermember comprises a material containing at least PTFE, drive efficiencyof a motor can also be improved.

With the above examinations, an alternative material of a fluorine resinsuch as a perfluoroalkoxy fluoroplastic (PFA) or anethylene-tetrafluoroethylene copolymer (ETFE). The content of thefluoroplastic preferably falls within the range of 3 to 1000 wt. %,andmore preferably, is 30 wt. % or more.

As for the durability, only the slider member No. 6 is much superior toother slider members, i.e., has a durability-limit rotation count of80,0000 reversible rotations. Such superiority is caused by the factthat the slider member No. 6 has a content of a material of a lowcoefficient of friction (PTFE) as very high as 80 wt. %, and alsocontains a lubricant material, i.e., molybdenum disulfide. In thismanner, when a slider member is formed by filling above 1 to 20 wt. % ofa lubricant material (molybdenum disulfide) in a base containing 50 wt.% or more of a material of a low coefficient of friction (PTFE), thusobtaining a motor having high efficiency, wear resistance, anddurability.

As for only the durability, with the above examinations, an alternativelubricant material such as carbon may be considered in addition tomolybdenum disulfide described above. The content of such a lubricantmaterial preferably falls within the range of 1 to 20 wt. % and morepreferably, is about 10 wt. % in order to attain lubricity.

Sticking can be reasoned by the relationship between a materialconstituting the slider member and a stator material. More specifically,the slider member No. 6 is formed by filling an inorganic material,i.e., a glass fiber which originally has almost no sticking property inaddition to materials free from sticking with respect to a fluoroplastic(PTFE) and a lubricant material (molybdenum disulfide). Since a statoremploys an invar material which is resistant against a chemical changesuch as rusting in combination with the above-mentioned slider member, asticking reaction never occurs when the slider member and the stator arecombined.

In combinations of the slider member No. 6 and stators of materialsother than the invar material (phosphor bronze and SUS301), sticking orsticking tendency is observed since phosphor bronze is not resistantagainst a chemical change and SUS301 is also not so resistant against achemical change as compared to the invar material. Sticking of theslider member No. 5 is caused by the sticking property of the EKonolE101 contained therein.

As for only sticking, with the above examinations, alternative materialsof inorganic materials such as titanium oxide, potassium titanate, andthe like may be used in addition to the above composition.

As described above, according to the embodiment of the presentinvention, a slider member of a rotor driven by a stator formed of anickel-iron alloy is formed to contain 3 to 100 wt. % of afluoroplastic, so that a motor having high efficiency and wearresistance as shown in TABLE 2 can be provided, and is suitable for aproduct which is required to be used over a long period of time.

If a slider member is formed of a material containing a fluoroplastic(50 wt. % or more) and a lubricant material (1 to 20 wt. %), a motorhaving high efficiency, wear resistance, and durability can be provided.

Furthermore, if a slider member is formed of a material containing afluoroplastic (3 to 80 wt. %), a lubricant material (1 to 20 wt. %), andan inorganic material (1 to 30 wt. %), a motor which has highefficiency, wear resistance, and durability, and which is free fromsticking between a stator and a slider member can be provided. The motoris suitable for a maintenance-free product such as a camera. When themotor is used in a maintenance-free product such as a camera, stickingis most important in the test items. In this case, a material formed ofonly a sticking-free material such as the slider member No. 6 ispreferable.

Other embodiments of the present invention will be described below withreference to FIGS. 7 to 9.

FIG. 7 is a sectional view showing an ultrasonic motor according to thepresent invention. A first electrode 13 is formed on an upper surface ofa piezoelectric member 12 constituting a stator 10, and secondelectrodes 14a and 14b are formed on its lower surface. A conductiveelastic member 11 is coupled to the piezoelectric member 12 so as to beelectrically connected to the electrode 13. The electrodes 14a and 14bare connected to lead wires 15 and 16 in the same manner as in FIGS. 10and 11. The elastic member 11 is formed of a conductive material such asphosphor bronze, stainless steel, or invar.

A flange-like support member 300 radially extends from the outerperipheral surface of the elastic member 11 near a neutral surface ofthe stator 10 as a whole by integral molding. The support member 300 hasa thin plate portion 301 contiguous with the outer peripheral surface ofthe elastic member 11 and having a thickness of about 0.3 mm, and athick portion 302 contiguous with the thin plate portion 301. Thethickness of the thick portion 302 is sufficiently larger than that ofthe thin plate portion 301. A male thread is formed on the peripheralsurface of the thick portion 302, and is threadably engaged with afemale thread formed on the inner peripheral surface of an annularfixing member 53, thereby fixing and holding the elastic member 11. Theother end of a lead wire 17, one end of which is grounded, is mounted onthe upper surface of the thick portion 302 by a screw 52.

A rotor 20 is constituted by adhering an annular slider member 22 to anannular rotor base 21. A flange portion 21a radially projects from aportion of the rotor base 21 near a neutral surface of the rotor as awhole, and a support member 54 is integrally molded on the peripheraledge of the flange portion 21a. A compression force generated by acompression means (not shown) is transmitted to the rotor 20 through thesupport member 54, thereby urging the lower surface of the slider member22 against a drive surface 11a of the elastic member 11.

In the above structure, the electrode 13 is grounded through the elasticmember 11, its support member 300, and the lead wire 17. As describedabove, a predetermined AC voltage is applied to the electrodes 14athrough the lead wire 15, and an AC voltage having a 90° phasedifference from the predetermined voltage is applied to the electrode14b through the lead wire 16. Upon application of these voltages, thepiezoelectric member 12 vibrates, and a traveling vibration wave isgenerated on the drive surface 11a of the elastic member 11. As aresult, the rotor 20 is driven. In this case, the thick portion 302 ofthe support member 300 is not vibrated since it is fixed to the fixingmember 53.

As described above, the support member 300 and the elastic member 11 areintegrally formed, and the lead wire 17 is connected to the thickportion 302 of the support member 300 to ground the electrode 13.Therefore, no conductive adhesive 18 (FIG. 10) is necessary. The thickportion 302 is not almost influenced by the vibration of thepiezoelectric member 12, and does not cause a grounding error due tovibration of the elastic member 11 unlike in the conventional structure.In addition, no undesirable vibration acts on the elastic member.

The thick portion 302 is not always necessary to prevent a groundingerror of electrodes as an object of the present invention. That is, thedistal end of the thin plate portion 301 may be fixed and held by afixing member. In the above structure, the lead wire 17 and the screw 52constitute a grounding means.

As shown in FIG. 8, a fixing member 55 may be formed of a conductivematerial, the grounding lead wire 17 may be fixed to the fixing member55 by the screw 52, and the electrode 13 may be grounded through theelastic member 11, a support member 303, the fixing member 55, and thelead wire 17.

In the above structures, the lead wire 17 is connected to the thickportion 302 or the fixing member 55 by the screw 52 but may be solderedthereto. A printed circuit board may be used in place of the lead wire17. In addition, the male thread is formed on the peripheral edge of thethick portion 302 or 305, and the threaded portion is threadably engagedwith the fixing member. However, the thick portion 302 or 305 may befixed to be vertically clamped by a pair of fixing members.

In the above structures, the support member 300 or 303 is formed on theouter peripheral surface of the elastic member 11. However, as shown inFIG. 9, a support member 306 may be formed on the inner peripheralsurface of the elastic member 11, and the support member may be fixed bya fixing member 56 inside the elastic member 11.

Other embodiments of the present invention will be described below withreference to FIGS. 12 to 16.

FIG. 12 is a perspective view of a rotor constituting an ultrasonicmotor according to the present invention, and FIG. 13 is a perspectiveview of a stator constituting the ultrasonic motor according to thepresent invention. A stator 100 comprises a ring-like elastic member 101of, e.g., phosphor bronze, stainless steel, invar, or the like, and aring-like piezoelectric member 102 adhered to the elastic member 101.Comb-like grooves 103 are formed at the side of a drive surface P1 ofthe elastic member 101.

A flange-like support member 309 is formed integrally with the elasticmember 101. The support member 309 comprises a thin plate portion 310radially projecting from the outer peripheral surface of the elasticmember 101 near a neutral surface of the stator 100 as a whole, and athick portion 311 integrally formed at the distal end of the thin plateportion 310. The thick portion 311 is fixed by a fixing member (notshown). A plurality of holes 312 are formed by etching in portions ofthe thin plate portion 310 located on extending lines of the comb-likegrooves 103.

A rotor 20 is constituted by adhering a ring-like slider member 22 to aring-like rotor base 21. A flange portion 21a radially projects from theouter peripheral surface of the rotor base 21 near a neutral surface ofthe rotor 20 as a whole. A support member 54 is integrally molded on theouter edge of the flange portion 21a. A compression force generated by acompression member (not shown) is transmitted to the rotor 20 throughthe support member 54, thus urging a lower surface P6 of the slidermember 22 against the drive surface P1 of the elastic member 101.

The operation of this embodiment will be described below.

When an AC voltage is applied to the piezoelectric member 102, thepiezoelectric member 102 causes bending-vibration, and a travelingvibration wave is generated in the drive surface P1 of the elasticmember 101. The vibration wave drives the rotor 20. In this case, sincea portion of the elastic member 101 formed with the comb-like grooves103 has a smaller thickness than those of other portions, this portionserves as a bending portion of the vibration wave. In this case, sincethe neutral surface of the stator 100 is located below as compared to acase without the grooves 103, the amplitude of the vibration wave isincreased, thus improving drive efficiency of the rotor 20.

Since the holes 312 are formed in portions of the thin plate portion 310of the support member 309, which are located on extending lines of thecomb-like grooves 103, the following advantages are obtained.

Since the portion of the elastic member 101 with the grooves 103 servesas the bending portion of the vibration wave, the portions of the thinplate portion 310 located on the extending lines of the grooves 103 alsoserve as bending portions. Since the holes 312 are formed at the bendingportions, a bending strength of these portions is decreased, and theseportions can be easily bent, thus increasing an amplitude. This alsocauses a decrease in support loss and improvement of drive efficiency ofa motor. FIG. 14 shows vibration amplitudes of respective portions ofthe stator 100 in the radial direction. In FIG. 14, a curve l1represents a case wherein the holes 312 are formed in the thin plateportion 310, and a curve l2 represents a case wherein no holes 312 areformed. As can be seen from FIG. 14, vibration amplitudes of respectiveportions with the holes 312 can be increased as compared to thosewithout holes.

Since the bending strength of the support member 309 is decreased,vibration is never externally transmitted through the support member309, thus preventing noise. In this embodiment, since the holes 312 areformed by etching, no residual stress is produced in the support member309.

In the above structure, the holes 312 are formed at positions on thethin plate portion 310 on the extending lines of the comb-like grooves103. However, the holes 312 need only be regularly formed in thecircumferential direction of the support member 309, and morepreferably, need only be regularly formed in association with thewavelength component of the traveling vibration wave generated in theelastic member 101. If the holes 312 are regularly formed in associationwith the cycle of the comb-like grooves 103, they can provide theabove-mentioned effect. FIGS. 15A to 15G show another embodiment ofholes 312 formed in the thin plate portion 310 in the relationshipbetween a traveling vibration wave and the comb-like grooves 103. FIG.15A is a chart of a traveling vibration wave, and FIG. 15B showscomb-like grooves. Eight comb-like grooves are formed within onewavelength component of the traveling vibration wave. FIGS. 15C to 15Gshow thin plate portion patterns of a support member. FIG. 15C shows apattern wherein holes corresponding in number to the comb-like groovesare aligned at equal intervals in the circumferential direction so thatthe centers of the grooves and holes coincide with each other. With thispattern, a support loss can be minimized. FIG. 15D shows substantiallythe same pattern as in FIG. 15C except that the centers of the comb-likegrooves and the holes do not coincide with each other. FIG. 15E show apattern wherein every other holes in FIG. 15C are formed. FIG. 15F showsa pattern wherein the holes are aligned in units of half wavelengths ofthe traveling vibration wave. FIG. 15G shows a pattern wherein each holehas a modified shape other than a circle.

As shown in FIG. 15G, the shape of each hole 312 is not limited to acircular or rectangular shape, but may be an elliptic shape or any othershapes.

In the above description, the support member 309 is formed on the outerperipheral surface of the elastic member 101 but may be formed on itsinner peripheral surface. Furthermore, the holes 312 are formed asthrough holes. However, the holes may be formed as recessed grooves 316,as shown in FIG. 16. That is, in the present invention, the hole meansnot only a through hole but also a non-through recessed groove (FIG.16), a dimple, and the like.

Still another embodiment of the present invention will be describedbelow with reference to FIG. 2.

As shown in FIG. 2, after a piezoelectric member 102 is adhered to ajunction surface P2 of an elastic member 101, an adhesive 400 is appliedto upper and lower end faces P4 and P3 of a thick portion 32 of asupport member 30, a surface P7 of a fixing cylinder 50, and a surfaceP5 of a pressing 40, and the pressing 40 is threadably engaged with thefixing cylinder 50 so that the surfaces P7 and P4, and the surfaces P5and P3 are brought into contact with each other. Thus, the thick portion32 is vertically clamped and fixed by the fixing cylinder 50 and thepressing 40. At this time, the lower end face P3 of the thick portion 32and the surface P5 of the pressing 40 are polished, and the adhesivebetween the surfaces P7 and P4 and between the surface P5 and the endface P3 serves as a filler. Therefore, the flatness of the drive surfaceP1 of the elastic member 101 will not be degraded. Therefore, thesupport member 30 integrally provided to the stator 100 is adhered tothe fixing cylinder 50 and the pressing 40 and is clamped by thecylinder 50 and the ring 40, so that a support loss can be reduced andreliability can be improved. In addition, since external transmission ofvibration can be prevented, noise can be stopped.

As shown in FIG. 5, when a support member 36 is formed on the innerperipheral surface of an elastic member 10, an adhesive 400 can befilled between a thick portion 38 and a pressing 41 and a fixingcylinder 51 when it is clamped by the pressing 41 and the fixingcylinder 51, thus obtaining the same effect a described above.

We claim:
 1. An ultrasonic motor which comprises:a stator having apiezoelectric member which is vibrated by a drive signal, and an elasticmember, a junction surface of which is coupled to said piezoelectricmember, and which generates a traveling vibration wave in a drivesurface thereof upon vibration of said piezoelectric member; a rotorwhich is urged against the drive surface of said elastic member and isdriven by the generated traveling vibration wave; a support memberhaving a thin plate portion contiguous with an outermost peripheralsurface of said elastic member, and a thick portion contiguous with anouter peripheral edge of said thin plate portion and having a largerthickness than that of said thin plate portion, said support memberprojecting integrally from said elastic member; and means engaging saidthick portion for fixing and supporting said support member, wherein oneend face of said thick portion is formed at the same level as thejunction surface of said elastic member.
 2. An ultrasonic motoraccording to claim 1, wherein said support member and said elasticmember are integrally molded.
 3. An ultrasonic motor according to claim1, wherein said means for fixing and supporting said support membercomprises means for clamping said thick portion between a first surfaceengaging said one end face of said thick portion and a second surfaceengaging an opposite end face of said thick portion.
 4. An ultrasonicmotor according to claim 3, wherein said first surface is an externalsurface of a pressing member and said second surface is an internalsurface of a fixing member.
 5. An ultrasonic motor according to claim 4,wherein said pressing member is threaded into said fixing member.
 6. Anultrasonic motor according to claim 5, wherein the thickness of saidpressing member is greater than the thickness of a portion of saidfixing member on which said second surface is formed.
 7. An ultrasonicmotor according to claim 1, wherein said one end face of said thickportion and the junction surface of said elastic member aresimultaneously flattened so as to be formed at the same level.
 8. Anultrasonic motor according to claim 1, wherein each of said junctionsurface and said drive surface has substantially the same degree offlatness.
 9. An ultrasonic motor which comprises:a stator having apiezoelectric member which is vibrated by a drive signal, and an elasticmember, a junction surface of which is coupled to said piezoelectricmember, and which generates a traveling vibration wave in a drivesurface thereof upon vibration of said piezoelectric member; a rotorwhich is urged against the drive surface of said elastic member and isdriven by the generated traveling vibration wave; a support memberhaving a thin plate portion contiguous with a peripheral surface of saidelastic member, and a thick portion contiguous with a peripheral edge ofsaid thin plate portion and having a larger thickness than that of saidthin plate portion, said support member projecting integrally from saidelastic member; and means engaging said thick portion for fixing andsupporting said support member, wherein one end face of said thickportion is formed at the same level as said junction surface of saidelastic member, and an opposite end face of said thick portion is formedat the same level as said drive surface of said elastic member.
 10. Anultrasonic motor according to claim 9, wherein said support member andsaid elastic member are integrally molded.
 11. An ultrasonic motoraccording to claim 9, wherein said one end face of said thick portionand said junction surface of said elastic member are simultaneouslyflattened, and wherein said opposite end face of said thick portion andsaid drive surface are simultaneously flattened.
 12. An ultrasonic motoraccording to claim 9, wherein said thin plate portion of said supportmember is contiguous with an outermost peripheral surface of saidelastic member.
 13. An ultrasonic motor which comprises:a stator havinga piezoelectric member which is vibrated by a drive signal, and anelastic member, a junction surface of which is coupled to saidpiezoelectric member, and which generates a traveling vibration wave ina drive surface thereof upon vibration of said piezoelectric member; arotor which is urged against the drive surface of said elastic memberand is driven by the generated traveling vibration wave; a supportmember having a thin plate portion contiguous with an innermostperipheral surface of said elastic member, and a thick portioncontiguous with an inner peripheral edge of said thin plate portion andhaving a larger thickness than that of said thin plate portion, saidsupport member projecting integrally from said elastic member; and meansengaging said thick portion for fixing and supporting said supportmember, wherein one end face of said thick portion and said junctionsurface of said elastic member are formed at the same level.
 14. Anultrasonic motor according to claim 13, wherein said one end face ofsaid thick portion and said junction surface of said elastic member aresimultaneously flattened to be formed at the same level.
 15. Anultrasonic motor according to claim 13, wherein each of said junctionsurface and said drive surface has substantially the same degree offlatness.
 16. An ultrasonic motor according to claim 13, wherein saidmeans for fixing and supporting said support member comprises means forclamping said thick portion between a first surface engaging said oneend face of said thick portion and a second surface engaging an oppositeend face of said thick portion.
 17. An ultrasonic motor according toclaim 16, wherein said first surface is an external surface of apressing member and said second surface is an internal surface of afixing member.
 18. An ultrasonic motor according to claim 17, whereinsaid pressing member is threaded onto said fixing member.
 19. Anultrasonic motor according to claim 18, wherein the thickness of saidpressing member is greater than the thickness of a portion of saidfixing member on which said second surface is formed.
 20. An ultrasonicmotor which comprises:a stator having a piezoelectric member which isvibrated by a drive signal, and an elastic member, a junction surface ofwhich is coupled to said piezoelectric member, and which generates atraveling vibration wave in a drive surface thereof upon vibration ofsaid piezoelectric member; a rotor which is urged against the drivesurface of said elastic member and is driven by the generated travelingvibration wave; a support member having a thin plate portion contiguouswith an outermost peripheral surface of said elastic member, and a thickportion contiguous with an outer peripheral edge of said thin plateportion and having a larger thickness than that of said thin plateportion, said support member projecting integrally from said elasticmember; and means engaging said thick portion for fixing and supportingsaid support member, wherein said means for fixing and supporting saidsupport member comprises a member into which said thick portion isthreaded.
 21. An ultrasonic motor according to claim 20, wherein each ofsaid junction surface and said drive surface has substantially the samedegree of flatness.
 22. An ultrasonic motor according to claim 20,wherein the last-mentioned member has a flat surface engaging a flat endface of said thick portion.
 23. An ultrasonic motor according to claim22, wherein said end face of said thick portion and said junctionsurface of said elastic member are simultaneously flattened so as to beformed at the same level.